ZANZIBAR, Tanzania – The Islamist forces in Somalia expanded their offensive yesterday, witnesses said, and began attacking the seat of the transitional government from a new direction.

While the fighting seemed to calm down in the initial hot spots, residents north of Baidoa, where the transitional government is based, said Islamist forces rushed in with several dozen pickups bristling with heavy guns. Before this, their attacks had been limited to the east and southwest of Baidoa, where they suffered many casualties.

Meanwhile, in Mogadishu, the seaside capital of Somalia and the Islamists' stronghold, the Islamist defense chief put out a public call for Muslim fighters to join the war against the transitional government and the Ethiopian forces protecting it. The Islamists vowed to turn their country into a third front of jihad, after Afghanistan and Iraq.

“Our country is open to Muslims worldwide,” said the defense chief, Yusuf Mohamed Siad.

Several thousand already have arrived, according to U.N. officials, who have said that mercenaries from Eritrea, Yemen, Syria and Libya have been streaming into Somalia for several months. On Friday, residents of Mogadishu reported seeing boatloads of armed men landing on the city's beaches.

Four days into the fighting, it was still not clear how many people have been killed, with casualty estimates ranging from a few dozen to several hundred – and both sides claim to be winning. Government forces seem to have captured several Islamists, because residents in Baidoa have seen blindfolded fighters driven away on military trucks. The Islamists, on the other hand, have threatened to kill their prisoners.

The heavy fighting started Wednesday when the Islamist forces, who control most of south-central Somalia, attacked the transitional government troops from two directions. The Islamists have said their grudge is not with fellow Somalis but with the Ethiopian troops in and around Baidoa.